Treating nodular iron



June 28, 1955 G. VENNERQOLM Em 2,11

TREATING NODULAR IRON Filed 001;. 9, 1950 G. l/ENNERHOLM R A MAN PATTE/VATTORNEYS nited States Patent T TREATING NODULAR IRON Gosta Vennerholm,Dearborn, and Royal Arch Van Patten, Garden City, Mich, assignors toFord Motor Company, Dearborn, Mich., a corporation of DelawareApplication October 9, 1950, Serial No. 189,133 claims. C1. 75-53 Thisapplication is concerned with the founding industry and moreparticularly with a method for improving the physical properties ofnodular cast iron. This socalled nodular iron has received recentwidespread publicity both in the current and patent literature and it isthought to be unnecessary to describe it further other than to statethat it may be produced by adding surficient magnesium to an appropriategray iron melt to produce a magnesium residual of about 0.05% andinoculating the melt just prior to pouring into the mold with any of themany commercially available graphitizing inoculants. This treatment, ifproperly carried out, will result in an as cast product in which theuncombined carbon is present in the form of spherulites or nodulesrather than the flaky form which is characteristic of typical gray iron.The matrix may be either ferritic or pearlitic, depending upon theanalysis and casting conditions. As is now well understood in the art,the absence of flaky graphite permits the production of the castinghaving a much higher tensile strength and ductility than ordinary grayiron.

The production of nodular iron castings particularly in highly irregularshapes has been impeded by the persistent occurrence of a phenomenonreferred to in the industry as cope defects. This name has been appliedbecause of the tendency of this defect to occur at the upper portion ofthe castings. A casting seriously weakened by these cope defects maypresent to the eye a perfect surface and also appear radiographicallysound.

However, when fractured the castings will exhibit a large number ofinclusions of unknown composition. While the exact composition of theseinclusions is unknown, it is apparent that a large amount of graphite isincluded in their makeup. In a fracture, these inclusions are disclosedas planes of discontinuity varying in size from those barely visible tothe naked eye up to one quarter of an inch in diameter. These graphiteladen planes of discontinuity, of course, seriously weaken the castings.

These inclusions have been found particularly troublesome in the castingof crankshafts for internal combustion engines inasmuch as they tend tocongregate at the juncture of the pin bearing and check, which isprecisely the location of maximum stress concentration at which fatiguecracks tend to develop.

It has been discovered that this phenomenon of cope defects can besubstantially eliminated by the application to the molten metal of anyof the many fluxes which have been developed for use with magnesium.

Particularly good results have been obtained with boric acid, borax,fused borax, and alkali metal fluoborates, as well as the fluxes whichare based upon the double chloride of an alkali metal and magnesium. Fora detailed description of commercially available fluxes, reference ismade to the Metals Handbook, 1948 edition, page 974.

While the inventors have not completely developed the theory underlyingtheir invention, it is their belief that Patented June 28, 1955oxidizing gases preferentially oxidize the magnesium content of themagnesium containing iron and that the resultant highly refractorymagnesium oxide is responsible for the occurrence of cope defects.

To eliminate these cope defects, the inventors intimately contact themagnesium type of flux with the molten magnesium containing iron.nomical and satisfactory method of applying these magnesium type fluxesto the molten metal is the contacting of the molten metal with a porousrefractory body which has been impregnated with the magnesium flux.These flux impregnated refractory bodies may readily be prepared by theimmersion of the completed refractory body in molten flux. Converselythe fiuxing metal could be included in the original refractory mix or inthe case of water-soluble fluxes, it could be applied by dipping thefinished refractory in a strong solution of the flux and drying.

In the application of this process, the inventors have been singularlysuccessful in the production of an internal combustion engine crankshafthaving the following composition:

Per cent Carbon 3.50-3.80 Silicon 2.20-3.00 Manganese 0.30-1.00Phosphorus 0.100 Sulphur 0.017 Magnesium 0.050 Iron Remainder along theline 2-2 in Figure 1.

As can be readily seen from the drawings the refractory form comprises abody which is circular as seen in the plan view and in section isisosceles trapezoid. A number of holes are provided in this form. Theaxes of these holes are parallel to the axis of the body. It is understood that this body is impregnated or coated with a magnesium typeflux. This refractory is incorporated in the mold in such a way that allof the metal which will eventually become a part of the finished castingmust pass through the holes in the refractory body. The passage of themolten metal through the relatively large number of holes causes asufliciently intimate contact between the flux and the molten metal toresult in the substantially complete elimination of the cope defects.

While the particular form of refractory shown in the drawings has beenfound to be highly satisfactory for applying the magnesium type flux tothe molten metal, the invention is by no means so limited. A refractorybody impregnated or coated with magnesium flux may be incorporated inthe mold and located so that the metal entering the mold will flowacross the refractory body. Also the ladles or other refractory linedfacilities employed in handling the molten magnesium treated metals maybe given a wash with molten magnesium flux which will coat and to someextent impregnate them with flux. The use of ladles so treated willresult in sufficient contact between the fiux and the molten metal tosubstantially reduce the occurrence of cope defects. Alternatively anordinary refractory fire brick may be impregnated with magnesium fluxand floated in the molten metal While in the ladle or other handlingapparatus.

We claim as our invention:

1. The process of producing nodular iron castings comprising adding toan appropriate melt sufiicient magnesium to produce an as cast nodularstructure and contacting this magnesium bearing melt with a refractory Aparticularly ecosubstance, said refractory substance including amagnesium type flux.

2. The process of producing nodular iron castings comprising adding toan appropriate melt sufficient magnesium to produce an as cast nodularstructure and contacting this magnesium bearing melt with a refractorysubstance, said refractory substance including a flux selected from thegroup consisting of borax, fused borax, boric acid, alkali metalfluoborates and mixtures comprising magnesium chloride and an alkalimetal chloride.

3. The process of producing nodular iron castings comprising adding toan appropriate melt suflicient magnesium to produce an as cast nodularstructure and contacting this-magnesium bearing melt with a refractorysubstance, said refractory substance having been coated with a magnesiumtype flux.

4.' The process of producing nodular iron castings comprising adding toan appropriate melt suflicient magnesium to produce an as cast nodularstructure and contacting this magnesium bearing melt with a refractorysubstance, said refractory substance having been coated and impregnatedwith a magnesium type flux.

5. The process of producing nodular iron casting comprising adding to anappropriate melt suflicient magnesium to produce an as cast nodularstructure and contacting this magnesium bearing melt with a refractorysubstance by flowing the molten metal over the refractory substance,said refractory substance carrying a magnesium type flux.

6. The process of producing nodular iron castings comprising adding toan appropriate melt sufiicient magnesium to produce an as cast nodularstructure and pouring this magnesium bearing melt through a perforaterefractory substance, said refractory substance carrying a magnesiumtype flux.

7. The process of producing nodular iron casting comprising adding to anappropriate melt sufficient magnesium to produce an as cast nodularstructure and pouring this magnesium bearing melt through a perforaterefractor y substance, said refractory substance carrying a magnesiumtype flux and being located in the mold in which the casting is poured.

8. The process of producing nodular iron castings comprising adding toan appropriate melt sufiicient magnesium to produce'an as cast nodularstructure and handling this magnesium in refractory vessels therefractory portions of which carry a magnesium type flux.

9. The process of producing nodular iron castings comprising adding toan appropriate melt suflicient magnesium to produce an as cast nodularstructure and floating in this melt a refractory substance which carriesa magnesium type flux.

10. The process of producing nodular iron castings comprising adding toan appropriate melt sufiicient magnesium to produce an as cast nodularstructure and casting this melt in molds, said molds containing arefractory body carrying a magnesium type flux and located so that themelt entering the mold will flow over said body.

No references cited.

7. THE PROCESS OF PRODUCING NODULAR IRON CASTING COMPRISING ADDING TO ANAPPROPRIATE MELT SUFFICIENT MAGNESIUM TO PRODUCE AN AS CAST NODULARSTRUCTURE AND POURING THIS MAGNESIUM BEARING MELT THROUGH A PERFORATEREFRACTORY SUBSTANCE, SAID REFRACTORY SUBSTANCE CARRYING A MAGNESIUMTYPE FLUX AND BEING LOCATED IN THE MOLD IN WHICH THE CASING IS POURED.